1. Field of the Invention
The subject invention is directed generally to a system for regulating fluid flow, and more particularly, to a system for regulating the flow of fuel from a variable displacement pump utilizing bypass flow.
2. Background of the Related Art
Fixed delivery fuel pumps have often been sized to provide excessive fuel flow capacity in order to insure adequate supply to the associated engine. Consequently, under many operating conditions, large amounts of pressurized fuel are returned to the pump inlet for recirculation. The return and recirculation results in significant fuel heating due to additional energy being put into the fuel which is subsequently turned into heat as the pressure drops in the recirculation path. In modern designs, fuel heating is a critical issue because the fuel is typically used as a heat exchanger to maintain proper operating temperature. Other methods of heat exchange are undesirable because of the associated size, weight and cost.
Variable displacement fuel pumps have partially overcome the drawbacks of fixed delivery pumps by being able to vary the amount of fuel output. By varying the fuel output, the fuel delivered more closely matches engine demand. Thus, the recirculated flow, along with the heat generated thereby, is reduced. Variable displacement fuel pumps are known in the art, as disclosed in U.S. Pat. No. 5,833,438 to Sunberg, the disclosure of which is herein incorporated by reference in its entirety. A variable displacement pump typically includes a rotor having a fixed axis and pivoting cam ring. The cam ring position may be controlled by a torque motor operated servo valve. However, the engine operating conditions often include transients such as those caused by engine actuator slewing, start-up and the like as would be appreciated by those of ordinary skill in the pertinent art. Under such rapidly varying operating conditions, prior art pump control systems have been unable to respond quickly and adequately. So despite this, variable displacement pumps still do not respond quickly enough to varying engine demands so excess fuel flow is still common.
In view of this shortcoming, control systems to fully utilize variable displacement fuel pumps have been developed. Examples of variable displacement pump control arrangements are disclosed in U.S. Pat. No. 5,716,201 to Peck et al. and U.S. Pat. No. 5,715,674 to Reuter et al., the disclosures of which are herein incorporated by reference in their entirety. Typical pump control systems attempt to maintain accurate fuel flow throughout the range of engine operating conditions. However, such systems still contain inadequacies such as instability, insufficient bandwidth. Moreover, such systems are still prone to delivering excessive fuel which must be recirculated. The pump control systems may include sophisticated electronics and numerous additional components to undesirably increase costs and complicate the pump control system.
In view of the above, it would be desirable to provide a pump control system which accurately and quickly regulates the output flow of a variable displacement pump without the associated drawbacks of the prior art.